Mold



MOLD

Filed May 1. 1941 2 Sheets-Sheet .1

F'IGZ.`

Mh/w@ A TTOHNE Y June 20, 1944. i R, 1 DETJEN 2,352,083

MOLD

Filed May 1', 1941 2 sheets-sheet 2 l' N VE NTOH s HomTL. DETJEN BYwM/QM@ A TTORNE Y Patented Jene-20,1944 2,352,083/

UNITED STATI-:s PATENT orifice MOLD Robert L.. Detjen, St. Louis, Mo., assignor, by mesme assignments, to Vincil R. Stamm. Walter J. Bach, and Roy 0. Bach. all of'St. Louis County, Mo., doing business' as Fixture Products Co., St. Louis, Mo.

Application May 1, 1941, Serial No. 391,239

3 Claims. (Ci. 18-39) My invention relates to the art of molding, and more particularly to improvements in molds for casting objects in plaster or other materials having similar molding properties.

which leaves substantially no seam lines or other blemishes on the castings, -thereby avoiding the necessity for repairing or"touohing up the castings after they are removed from the mold.

AnotherL advantage of my improved mold is that the split or parting line is notrequired to be located at any particular wall area-a customary requirement in molds of former type which sometimes results in the formation of a. seam in a prominent surface portion of the castingbut may be located so as' -to subtend a relatively inconspicuous surface portion of the cast object.

Yet another advantage is that the mold of my invention is not adversely affected by heat such as is normally chemically produced in plaster during the hardening process. A plaster casting may be allowed to remain in the mold of my in vention until it hardens sufficiently to permit its safe removal.

These and other objects and advantages will appear and be more fully explained in the following description wherein reference is made to the accompanying drawings. In these drawings:

Fig. 1 is a rear elevational view of a pattern or model having certain provisions useful in the formation of a matrix;

Fig. 2' is a side elevational view of the pattern of Fig. l with the matrix member of my improved mold thereon;

inforce the matrix member of Fig. 5 during a molding operation;

Fig. 7 shows the sneu and matrix members in assembled relation, and

Fig. 8 is a transverse sectional view taken at line 8-0 of Fig. '1.

Referring now to the drawings by characters of reference, my improved mold comprises a rel- The principal object of my invention is to elimi- 5 atively thin-walled, flexible rubber envelope, connate many of the undesirable conditions and disstituting the matrix, and a rigid, sectionalized I advantages attending the use of molds of hereshell which is adapted to fit about said matrix tofore prevailing type by the provision of an imto reinforce and hold it in proper shape during proved mold which is very durable. being adapted a molding operation. to produce a great number of identical castings l0 'I'he rubber matrix, shown in Fig. 5 and desigwithout appreciable wear; which is capable of nated it, is made on'a pattern or model characreproducing delicate details of a pattern in the terized by a thin flange that extends longitudieastings, and which retains such details in spite nally of the pattern body and projects a distance 'a of frequent use. of three-fourths ofan inch or more therefrom. Other objects are attainedinanimproved mold 35 In the present example the pattern il selected for illustration is a bust such as is employed for millinery display purposes. The flange I2 aforesaid, comprises a stripof sheet metal and extends substantially the full height, at the back of the pattern. It is desirable to install the flange i2 without unduly altering the normal surface contour of the pattern body, and this may be accom-l plished by producing a saw-cut in the pattern, inserting the flange member to the desired depth, and cementing the flange in place. In most instances it will be advantageous to locate the with the matrix, by which the mating edges of the slit are held together, and the opening sealed during a molding operation. A groove i4 or the like in flange i2 produces complementary tongue and groove portions i5 and I6 in the opposed lips i3, which facilitates proper registration and fitting together of the lips.

The body of the pattern is mounted on a base member il to give it stabilityand to provide a surface for the formation of a rubber base flange is that skirts the opening I9 through which the mold is adapted to be charged, as `will hereinafter more fully appear. The entire pattern, irl-A cluding the flange t2 and the base member il, is coated with a suitable paint or lacquer to render it substantially impervious Ato moisture and provide for a uniform surface texture.

The rubber matrix it is molded about the pat- B0 tern by applying successive layers of'rubber, in a liquid state, over the entire surface of the pattern body il, the flange I2 and the upper surface of base member il. each layer` being allowed to set before a subsequent layer is applied. 'Ihe pattern thusly coveredls illustrated in Fig. 2.

matrix. Y

'Ihe rubber may be applied b y brushing or spraying, the latter method being preferred, and a sufficient number of coats is applied to build up a layer or wall thickness of approximately threesixteenths of an inch. After the last coat has set sufficiently to permit the matrix to be handled, the rubber on the upper surface of the base member I1 is appropriately trimmed to form a base flange of the desired width. Next, 'a knife out. indicated at 20, is made in the rubber at the outer edge of flange I2 and extended the full length thereof. 'I'his cut permits the rubber lip portion I3 on the opposite sides of flange I2 to be separated, and the layer of rubber to be stripped. or peeled from the pattern. It has been found desirable to remove the matrix from the pattern in this manner before the rubber has completely dried or set. and since the rubber may still be in a somewhat plastic condition great care must be exercised to avoid wrinkling, creasing or otherwise impairing the matrix. After its removal as aforesaid the matrix is placed in a suitable curing or drying atmosphere, wherein it is supported in a suitable manner to prevent itfrom losing its shape before it has thoroughly cured.' Thus. by suspending the matrix by a cord attached to the upper portion of the lips I3, and allowing the base ange I8 to rest on a support, the weight of the matrix will be'distributed, avoiding stresses that tend to distort the matrix during the drying process.

The matrix produced by the foregoing method is very pliable, yet has sufficient body that it will retain its proper shape and form when supported as aforesaid. It is quite possible to produce a rubber matrix of such thickness and body that extraneous means to hold it in proper shape are not required. For example,"merely by applying a suflicient number of coats of the liquid rubber onto the pattern, a matrix having a wall thickness of one-half inch or more may be produced. Such relatively thick-walled rubber molds are known in the art but have never been satisfactory except, perhaps, for the molding of simple shapes. The chief reason for this resides in the dimculty ordinarily experiencedcin removing the molded object, without damage thereto. from the rubber mold. such difficulty being increased where a one-piece mold is employed. I have determined that the most satisfactory method of separating the mold fromthe object cast therein is to peel the mold from the object. This, of course, cannot readily and satisfactorilybe accomplished unless the rubber mold is relatively thin andf highly flexible. Accordingly the rubber 'matrix of my invention has these characteristics, the wall being readily adapted to be doubled back upon itself as would normally occur when peeling the matrix from a casting.

It will be understood that a rubber matrix having the physical characteristics above described will not, of itself, have suflicient body" or stiffness to maintain its proper or normal shape, and to impart the same to a mass of plastic material introduced therein. Therefore reenforcing means in the form of rigid shell sections are used in conjunction with the described To form these shell sections the rubber matrix is used as a pattern and the material from which the shell is to be formed. plaster being suitable, is cast in place about the matrix. To facilitate holding the matrix in proper shape during its use asa pattern, as aforesaid, the `edges along the seam at the base of the lips I! are secured together by stitching, indicated at 2I (Fig. 5). It should be understood that such lstitching is merely a temporary expedient, the stitches,` being removed after the matrix has served its purpose as a pattern during the formation oi? the backing shell. The matrix is supported in a manner most conducive to maintaining it in proper shape and form, as by supporting it from above and below, and then plaster in a thin, watery state is applied, as by splashing the same on the matrix, Vto cover the surface thereof. The plaster is allowed to dry, producing a thin initialcoat. Several additional coats of thin plaster are applied and allowed to harden, whereafter a layer 2@ the matrix. The opposite side edges 3 of the shell section are suitably trimmed to render them smooth and regular. Key recesses 24 are cut into edge surfaces of the front section, and the entire edge surfaces are coated with a thin film of grease. The shell sections 26 and 21 are prepared in the manner above described, by rst splashing watery plaster on the exposed matrix surfaces to produce a thin shell, then increasing the thickness of the shell sections by subsequent layers of plaster and burlap. 'I'he thin iilm of grease on the edge surfaces 23 of section 22 prevent coalescence thereof with the subsequently formed sections 28 and 21 which are formed with projections or keys 28 that fit the recesses 24 of section 22 formed thereon.

other by the rubber flange formed by the matrix lips i3. Complementary groove and ridge formations 29 and 30 are produced on the opposite edge surfaces of the sections 26 and 21 by the corresponding formations I5 and I6 on the lips I3 of the matrix, and these formations, together with the key projections 28 and recesses 24 assure a proper fitting together of the shell sections and proper positioning of the matrix in the shell assembly.

In using the mold of my invention the rubber matrix is immersed in water and then installed in the outer shell, the assembly being illustrated in Fig. '7. The shell sections are held in assembled relation about the matrix by means of rubber bands 3|. or other suitable binding means.

It .will b e observed that the matrix lips I3 are tightly compressed together between the opposite surfaces of the sections 26 and 21 so that only the merest outline of the seam will be manifest on the casting. The matrix base flange I8 at the open end of the mold prevents plaster or other material from entering the crevice bew tween thev matrix and shell sections when the mold is being charged. As is customary in the casting of plaster objects, plaster in a thin, semi-- a5 inner surface of the matrix is coated. After thisinitial layer has set sufllciently, additional plaster is introduced to produce either a solid casting, or a hollow one of desired wall thickness. After a suitable interval to allow the plaster to harden, the rubber bands 3| are removed and the shell sections 22, 28 and 21 are lifted away from the casting and matrix member which envelops it. As has been previously mentioned, removal of the matrix is accomplished by openuN5 ing the seam at the lip portions I 3, then literally of thick plaster may be applied. Suitable reinv The sections 26 and 21 are separated from each y ermly f meile@ hollow, ette en e :e: eilt in e. well portion the:

l ey m easily removed im tli ce dimm. The mtriX is im :mi in Wagga' t@ remeve ell ti'eces of plaster and tb is ree@ to be liistelledin the sllells for subs .l use.

.en impatient advantage of the mold of e invention over the glue end gelatine mol eur rently in widespi'eetl uw is thet with melde el the lettei type it is deeble.. and in seme ew.

pemtlve. theft the plaster castles@ iemeved beote'they have herdened sumcientlv to permit them to be handled without :f-i oi breekege. Thus, the heet produced by the plestenwhlcii is exotlielc. dg the eetting proee, is likely te imr e glue or gelatine mold. Suela however is not the ease with'the rubber met or mold ...we of my invention. e object met' eine desirable is left ire the sell trie until it hes leerden@ tegame the stese oi fi' llallity,`

Weet E elelm eine deeire to secure l lettere Peteet le: V

i. En e melding elevice, e matrix comp fee :seid t said 1 poi'tlone ede@ te grip il @me e@ @me ee of seid slit te im; -eeeleli n= dition define e molding reilen.

2. In e elel device, e. met compi' f f seid metileg elem the opposite edges. el eei slit.

a rigid, seetieeelieed shell steuete edepted snugly te receive eel@ metrix te prevent lfieetleii of the metile., han.; e epeietlen, emi means im' haleine said sliell sections im. eese bled xeletlen eut seid matrix, en@ with d matrix .line tightly elemped together between opposite eeleee ei eeemt shell sections.

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